The present invention relates to read and write power control methods and system of an optical recording device used for recording information on an optical disk that had read-only areas.
Recently, various types of rewritable optical disk such as a DVD-RAM (Digital Versatile Disk Random Access Memory) or DVD-RW disks capable of reproducing digital data therein have come into wide use. In DVD-RAM disks, the stored information is consequently allocated in sector units. Each sector unit includes a read-only identification (ID) area (i.e. a header) and a rewritable area (i.e. user data area), as shown in FIG. 1A. The ID area, i.e. header, is embossed on the optical disk and can be read out with physical information data (PID) which is used to identify the physical location of the sector relative to the optical disk.
Referring to FIGS. 1A & 1B, a pick-up head of an optical recording device applicable for DVD-RAM disk might need to frequently meet multiple headers disposed on the DVD-RAM disk as long as a writing signal is set at logic high to order a write power for a recording operation of the pick-up head. Prior to meet each header, the writing signal has to be set at logic low to temporarily switch the power control from the write power induced by a write power control signal to a read power induced by a read power control signal. This could avoid crushing the PID stored in the respective headers and proceed as the reading operations on the headers, as shown in FIGS. 1C & 1D. However, the pick-up head needs an exact and stable read power to accurately read out the relative PID from the respective headers.
Further referring to FIGS. 1C & 1D, each level transition of a read or write power control signal, under a turn of the power control, for example, from either a write power to a read power, or from a read power to a write power, would result in a unstable power output initially for a while. This is because the read/write power control loop needs a period P1, P2 to settle signal levels from an initial level to approach an optimal level. Especially, if a difference/drop between the initial level and optimal level becomes enlarged because of an operating temperature rise, after each time of beginning of writing operation, the laser power emitted from the pickup head will be always unstable for a while.
However, for the storage optical disk with a header layout, e.g. DVD-RAM, it is a significant topic to achieve a steady power control and a great reading and writing qualities during frequent read/write power switches.
In a case of performing a read power control during a recording operation, shown in FIG. 1C, an operation temperature that may be successively rising would cause in an inexact level difference L1 of the read power control signal output. The read power control signal output has to be adjusted by an Auto Power Control (APC) circuit with compensating the read power control signal to approach the exact level for exactly reading data in the header. However a period of reading the header is too short insufficient to sample an exact power signal into a power control loop to generate a proper power, especially in a high, multiple speed operation.
In another case of performing a write power control during a recording operation, shown in FIG. 1D, the write power control would be frequently interrupted for each time when the pick-up head of the optical recording device passes over respective headers on the optical disk and has to be reactivated thereafter. However, the level transition of a write power control signal under different power control loop (i.e. a close or open loop) may be too long and insufficient to supply the pick-up head with a steady write power. Also, the operation temperature that may be successively rising would cause in an inexact level difference L2 of the write power control signal output. It is apparent that unstable write power is greater proportioned to be involved in writing quality, especially under a high operation temperature.